Telescopic steering shafts in motor vehicles make it possible to adjust the steering column, it being possible for the steering wheel position to be set in the longitudinal direction of the steering shaft. Moreover, the steering shaft can be pushed together in the case of a crash, which effectively prevents the steering column penetrating further into the interior of the passenger compartment and leading to injuries of the occupants. This is achieved as a rule by way of the provision of two shafts which can telescope with respect to one another, namely an outer shaft which is configured as a hollow shaft in the form of a tubular hollow profile, and an inner shaft which is mounted therein such that it can be displaced in the direction of the longitudinal axis of the steering shaft. The inner shaft and the hollow shaft together form a steering shaft which, by way of a telescoping relative movement of the shafts, can be shortened correspondingly by being pushed together or can be extended by being pulled out. The transmission of the torque which is introduced for steering purposes takes place via positively locking elements which engage into one another in a torque-transmitting manner, that is to say in a positively locking manner with regard to a rotation about the longitudinal axis, for example by way of a polygonal profile of the telescoping shafts or else positively locking elements which are inserted between the shafts, such as rolling bodies or the like.
A telescoping steering shaft is supplied and installed in the vehicle as a completely assembled module, in which the inner shaft is mounted in the outer shaft, that is to say is pushed into its opening cross section. In addition to normal operation, in which a steering column is adjusted in a controlled manner within the provided adjustment travel in order to set the steering wheel position, a steering shaft can be pulled apart in an uncontrolled manner in the direction of the longitudinal axis of the steering shaft, that is to say in the longitudinal direction, in the case of a repair of the vehicle, in the case of improper handling or in the case of transport, the inner shaft being pulled completely out of the hollow shaft and being separated from the outer shaft as a result. In the case of a safety-relevant component such as a steering column, unintentional dismantling of this type which leads to separation of the steering train has to be prevented reliably in any event. To this end, it is known to provide a securing apparatus in the form of a pulling-out limiting apparatus which limits the adjustment travel of the telescoping means and rules out a separation of the inner and outer shaft. In specific terms, to this end, a stop element is arranged in the opening cross section of the hollow shaft, which stop element comprises a stop face, the surface normal of which points in the longitudinal direction toward the hollow shaft, that is to say in the pushing-in direction of the inner shaft, as viewed from the inner shaft. The inner shaft can comprise a counterstop at its end, with a stop face which is directed counter to the stop element; in other words, its stop face engages behind the stop element with regard to the pulling-out direction.
In the prior art, CN201494492U has disclosed a securing apparatus, namely a pulling-out limiting apparatus, which is configured as a cap which is plugged onto that end of the outer hollow shaft which is directed toward the inner shaft and is fixed with regard to the longitudinal direction by way of positively locking engagement into a fastening groove which is configured in the outer side of the hollow shaft. The cap has a passage for the inner shaft, which passage is smaller than the opening cross section of the hollow shaft. As a result, a stop element with a stop face is provided by the cap in that opening of the hollow shaft which is covered partially by it, with which stop face, when the inner shaft is pulled out, a counterstop which is connected to or interacts with the inner shaft comes into contact and limits the pulling-out action, for example a head or projection which is arranged at the end of the inner shaft and is of greater cross-section than the passage of the cap, or else a positively locking element which is arranged between the inner and the outer shaft, such as a rolling body arrangement. Said cap has a relatively complicated multiple-piece construction and, on account of the fastening on the outer surface, projects to the outside beyond the outer cross section of the hollow shaft, which is disadvantageous during assembly, or requires complicated machining of the outer shaft.
DE 10 2009 000 432 A1 describes a securing apparatus of similar configuration. In said document, a holding cap is likewise proposed as pulling-out limiting apparatus, which holding cap is fixed in positively locking elements on the outer side of the outer shaft (hollow shaft). Said holding cap is also of multiple-piece configuration and engages around the hollow shaft from the outside. This requires corresponding machining, and the holding cap projects to the outside beyond the cross section of the outer shaft, which complicates the handling during assembly.
A disadvantage of the securing apparatuses which are known in the prior art is the complicated production and the unfavorable assembly capability.
In view of the problems explained in the preceding text, it is an object of the present invention to specify an improved steering shaft which comprises a securing apparatus for securing against pulling out, which securing apparatus is simple and can be assembled easily.